Baicalein has been reported to promote apoptosis and/or suppress cellular growth and proliferation of NSCLC cells. A study has shown that baicalein promotes sensitivity to cisplatin drugs in A549 and H460 cells by inducing apoptosis and inhibiting cell proliferation through suppression of the PI3K/Akt signaling pathway and the expression of microRNA 424-3p (miR-424-3p) targeting phosphatase and tensin homolog (PTEN) gene expression [56]. In another study, baicalein enhances antitumor activity by reducing the induction of vasculogenic mimicry (VM), a pattern of tumor microcirculation, via inhibiting the expression of VM-associated factors (e.g., MMP9, VE-cadherin) and the RhoA/rho-associated coiled-coil kinase (RhoA/ROCK) signaling pathway, leading to the suppression of motility and viability of A549 cells [57]. A study by Li et al. [58] reported that baicalein suppresses MAP4K3 expression via reducing its stability. The results also indicated that inhibition of the mTOR signaling pathway in A549 and H1299 cells by RNA interference could be sufficient in mediating baicalein-induced autophagy.

In a study carried out by Zhang et al. [59], the A549 and H1299 cells were treated with different concentrations of baicalein to study the mechanisms by which baicalein suppresses cell metastasis. The results showed that baicalein inhibits cell metastasis by inhibiting ezrin tension transduction, leader cell production and inducible nitric oxide synthase (iNOS)-mediated ezrin S-nitrosylation (SNO) tension, which are responsible for A549 and H1299 cell aggression in the inflammatory milieu. A study by Cathcart et al. [42] reported that the angiogenesis of NSCLC cells (A549, H460 and SKMES1) is significantly inhibited via downregulating VEGF-A, FGFR-2 and RB-1 expression. Su et al. [60] reported baicalein increases the protein expression of E-cadherin and inhibits the EMT-induced N-cadherin and vimentin in A549 and H1299 cells by downregulating the Notch signaling pathway. Similarly, a study on the anti-tumor effect of baicalein on NSCLC cells showed that baicalein causes an inhibitory effect on A549 cells by suppressing the expressions of N-cadherin, vimentin, VEGF-1, and upregulating the expression of E-cadherin through Src-Id1 signaling pathway blocking [43]. Therefore, baicalein showed effective results in the inhibition of NSCLC cells through anti-proliferative/metastatic, anti-angiogenesis and apoptosis/autophagy induction. The mechanisms underlying the effect are linked to the inhibition of different cellular signaling pathways.

A few in vitro studies have shown potent anti-lung cancer activity of baicalin in NSCLC cell lines. Zhang et al. [61] reported the anti-lung cancer activities of baicalin in A549 and H2009 cells at different concentrations, in combination with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a potential anticancer agent which modulates signaling pathways in NSCLC cells. Baicalin sensitizes lung cancer cells to TRAIL-induced apoptosis via the activation of MAPK and reactive oxygen species (ROS) production. Another study reported a high anti-lung cancer effect of baicalin in combination with DDP (cisplatin) on proliferation and invasion of A549 cells. Baicalin suppresses protein expression of microtubule affinity-regulating kinase 2 (MARK2) and Akt in A549/DDP cells, which are involved in cell proliferation and the pathogenesis of lung cancer [62]. Diao et al. [63] used baicalin to examine its inhibitory effect on NSCLC cells. The inhibitory effect of baicalin is observed against H441, H1975 and H1299 cells with a high expression level of PDZ-binding kinase/T-LAK cell-originated protein kinase (PBK/TOPK), a novel mitotic kinase which promotes cell invasion. You et al. [64] reported that baicalin stimulates apoptosis and inhibits the invasion abilities in A549 and H1299 cells. This is observed through activation of the sirtuin 1 gene/AMPK (SIRT1/AMPK) signaling pathway, known as tumor suppressor genes, and inhibition of the expression levels of MMP2 and MMP9 in NSCLC cells. From these studies, it can be suggested that baicalin has significant anti-proliferative/invasive and apoptotic effects, and the mechanisms of its therapeutic effect in NSCLC cells are related to the modulation of cellular signaling pathways.

Wogonin possesses antitumor properties against NSCLC cells, as demonstrated by a few in vitro studies. The study conducted by He et al. [65] found high anti-tumor activity against A549 cells of wogonin in combination with cisplatin. The anti-tumor effect of wogonin is reported as enhancing cisplatin-induced cell death through activating apoptosis, cleavage of the caspase-3 substrate PARP, caspase-3 and ROS production. Zhao et al. [66] assessed the inhibitory effect of wogonin in A549 cells by targeting the inflammatory microenvironment. The results demonstrated inhibition in human monocytic leukemia cell line (THP-1 CM)-induced migration of A549 cells, IL-6-induced EMT, vimentin, N-cadherin, Twist and Snail, and activation of E-cadherin. The inactivation of signal transducer and activation of the transcription 3 (STAT3) signaling pathway was found to be the mechanisms for this effect.

Wang et al. [67] performed a proliferation inhibition assay on A549 cells. The study reported a significant cell proliferation inhibition rate of 54% in A549 when treated with wogonin. Wogonin also showed an effect on energy metabolism by reducing lactate dehydrogenase (LDH) activity in A549 cells. In a study performed to assess the effect of wogonin on NSCLC cells and to explore their mechanism of action as an anti-tumor inhibitor, wogonin showed a significant cell viability inhibition rate of 31% and 34% in A549 and A427 cells, respectively. The mechanism of NSCLC cell inhibition is linked to the activation of apoptosis-inducing enzymes, autophagy and formation of ROS [68]. In the study by Chen et al. [69], the anticancer effects of wogonin in different concentrations on A549 cells are examined through regulating cellular pathways to assess cell viability. Results showed that wogonin inhibits cell viability and induces apoptosis in A549 cells through down-regulating HDAC1 and HDAC2 at mRNA and protein levels, and c-Myc oncogene, S-phase kinase-associated protein 2 (Skp2), F-box and WD repeat domain-containing 7 (Fbw7) and Glycogen synthase kinase 3b (GSK3b) at the protein level. A study of the inhibitory effect of wogonin on cell viability of NSCLC cells, Shi et al. [70] reported cell cycle arrest, senescence and apoptosis-induction in A549 cells by the downregulation of protein serum levels and glucocorticoid-inducible kinase 1 (SGK1). Furthermore, wogonin upregulates cellular levels of apoptotic protease activating factor-1 (APAF1), Bax, p21, promyelocytic leukemia protein (PML), growth arrest and DNA damage-inducible 45A(GADD45A) and yippee-like 3 (YPEL3) in A549 cells, which are the key factors involved in apoptosis, senescence and cell cycle arrest. Therefore, it can be suggested that wogonin has a strong anti-proliferative/viability, anti-inflammatory and apoptotic activities against NSCLC cells through regulation of several cellular signaling pathways as the mechanisms for these activities.

Studies that have examined the in vitro activities of wogonoside on NSCLC cells are limited. A study by Luo et al. [71] reported the inhibition of A549 cells via inducing apoptosis and cell cycle arrest when treated with wogonoside. Wogonoside treatment upregulates cleaved caspase-3/9 and Bax expression, downregulates Bcl-2 expression, and promotes the levels of mitochondrial cytochrome c in the cytosol of A549 cells. Furthermore, wogonoside induces apoptosis and cell cycle arrest by reducing phospho-mTOR and its downstream target p70S6K and increasing phospho-AMPK in A549 cells, suggesting that the AMPK/mTOR signaling pathway may be involved in the apoptotic activity of wogonoside. A study by Wang et al. [72] did not show any anti-proliferative effects of wogonoside on six cancer cell lines, including NSCLC (DMEM). However, the study observed the anti-proliferative activity on DMEM treated with wogonin (the deglycosylation of wogonoside).

A few in vitro studies have revealed that oroxylin A (OA) possesses strong anti-lung cancer activity in NSCLC cell lines. Shen et al. [73] studied the anti-inflammatory effect of OA on T_regs in the lung cancer environment by using the H460 cell line. The results of the study showed that OA inhibits T_regs production in H460 cells. Treatment with OA causes an inhibitory effect on the H460 cells cocultured with Jurkat cells by suppressing TGFβ-activated Smad3, ERK1/2, c-JUN NH2-terminal kinase (JNK) and p38 signaling pathways. OA also significantly inhibits the DNA binding activity of NF-κB/p65 in H460 cells by reducing phospho-Kappa B kinase α, β (IKKα, IKKβ). A study by Wei et al. [74] has been performed to assess the anti-invasive effect of OA on NSCLC cells and the molecular mechanisms involved. The study reported inhibition in A549 and 95-D cell migration/invasion with a 70% and 73% inhibition rate OA, respectively. The mechanism of inhibition is attributed to the suppression of Snail/TGFβ-induced EMT through ERK/Glycogen synthase kinase-3β (GSK-3β) signaling pathway blocking. As a result, OA downregulates expression of CD44v6, MMP-9, and vimentin and upregulates the expression of E-cadherin, and this could lead to the suppression of invasion and migration in Snail-expressing NSCLC cells. Another study by Wei et al. [75] reported the effect of OA on anoikis (cell death)-sensitization and glycolysis-inhibition in NSCLC cells. Results showed that OA suppresses the growth of detached A549 cells and induces anoikis through Src/PI3K/AKT signal pathway inhibition at the Tyr418 and ser316 sites. The study also showed that OA induces anoikis in A549 cells by lowering ATP synthesis, the level of glycolysis, lactic acid production and hexokinase II (HK II) glycolytic enzyme activity in mitochondria. A study by Liu et al. [76] was conducted to evaluate the effect of OA with cisplatin on suppression of NSCLC cells under hypoxic conditions. Flow cytometric and CCK8 assays reported that OA promotes cisplatin-induced cell death in H460 cells under hypoxia through inhibiting xeroderma pigmentosum group C (XPC), a DNA damage recognition protein upregulated by HIF-1α, which is implicated in the activation of nucleotide excision repair (NER). It is, therefore, suggested that OA has significant anti-invasive and anti-inflammatory activities in nicotine-induced NSCLC cells, due to their ability to inhibit cellular signaling pathways involved in NSCLC development. Taken together, S. baicalensis compounds possess anti-proliferative/metastatic/invasive, anti-inflammatory, anti-angiogenesis and apoptotic/autophagic properties (Figure 1). These compounds showed significant inhibition of NSCLC cells by suppressing/modulating the activity of cellular signaling pathways.